Researchers with IBM and North Carolina State University have come up with a way to patch security holes in virtual machines (VMs) even when these systems are offline, closing a potential security hole.

Existing patch management systems work with systems that are online, not dormant and not VMs. To date, it has been difficult to bring VM images online to patch them, the researchers say, and they are vulnerable during that window when they first go online unpatched. So the researchers built a tool called Nuwa, named after the Chinese goddess who patched a hole in the sky, which converts patches into ones that can be applied to offline VMs.

"We've designed a way to patch these virtual machines while they are offline so that they are kept up to date in terms of security protection," says Dr. Peng Ning, professor of computer science at NC State and one of the lead researchers on the project. "Current patching systems are designed for computers that are online, and they don't work for dormant computers or virtual machines. The tool we developed automatically analyzes the 'script' that dictates how a security patch is installed, and then automatically rewrites the script to make it compatible with an offline system."

Nuwa is based on technology developed by IBM called Mirage that handles large numbers of offline VM images. The tool basically saves one version of a file used by multiple VMs rather than saving the same file over and over for each individual VM. That way, multiple VMs can be patched simultaneously via that one file that they use.

According to the research, Nuwa sped up patching by more than four times that of an online method, and two to four times as fast when used with IBM's Mirage.

The research team -- which included Ning, Wu Zhou, and Ruowen Wang, all of NC State; and Xiaolan Zhang, Glenn Ammons, and Vasanth Bala of the IBM T.J. Watson Research Center -- deployed two prototypes. The first is a Nuwa tool that supports Debian and RPM package managers, and the second is a Mirage-based Nuwa that supports the RPM package manager.

They ran Nuwa in a cloud RC2 environment, as well: "Nuwa's safety analysis and script rewriting techniques are effective -- 1) Nuwa is able to convert more than 99% of the patches to safe versions that can then be applied offline to VM images; 2) the combination of offline patching with additional optimization made possible through Mirage allows Nuwa to be an order of magnitude more efficient than online patching; and 3) Nuwa successfully patched 278 images in a real compute cloud," the researchers wrote in their paper, which they will present next month at the Annual Computer Security Applications Conference in Austin, Texas.

Nuwa currently does not support offline patching of a "suspended" VM image (one that includes a "snapshot" of the memory state of the system plus its file system). "In our future research, we will investigate techniques to patch suspended VM images and how to perform offline patching on Windows platforms," the researchers wrote.

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